JavaScript programming through Matlab centroid algorithm positioning learning

As a closed commercial software, Matlab is controlled by the US government and ignores business ethics, so it is not recommended for use. If you like Matlab syntax, you can move to the open source octave, which has the same syntax as Matlab.

Matlab Centroid Algorithm

The so-called centroid is the center of gravity when the density is used as the grayscale value of the pixel. For example, the x coordinate of the centroid is

The most intuitive method is the following one.

%%Find the center of mass position of img through the center of mass algorithm function [x,y] = oCenter(img)
img = double(img);
[m,n] = size(img);
x = 0;y = 0;sum=0;
for i = 1:m
    for j = 1:n
        y = y + img(i,j)*i;
        x = x + img(i,j)*j;
        sum = sum+img(i,j);
    end
end
x = x/sum;
y = y/sum;

This is simple and crude enough, but it is too ugly. After all, in Matlab, matrix is ​​the most basic operation unit.
And in the process of accumulating and summing, the same array is indeed used repeatedly. For the i-th row, each column is multiplied by 1,2,3... and summed, which is the dot product of the i-th row vector and the vector [1:n] . So regardless of the entire picture, the centroid of the i-th row vector can be written out relatively simply.

x = img(i,:)*(1:n)'/sum(img(i,:));

Based on this, we also got an unexpected benefit, that is, we can easily write the centroid of each row in one line of expression

x = img*(1:n)'./sum(img,2);%The centroid of each row y = (1:m)*img./sum(img);%The centroid of each column

OCD means looking comfortable.
Accordingly, the centroid of the entire image can be written as

sumImg = sum(img(:));
x = sum(img)*(1:n)'/sumImg;
y = (1:m)*sum(img,2)/sumImg;

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